Epidemiologic, immunologic, and pathologic evidence has suggested that, in a significant number of cases, schizophrenia may be related to infection with or activation of a viral disease of the brain. To further pursue this possibility, we have extended our immunocytochemical and in situ hybridization studies of brain (in which we sought evidence of specific viral antigens or genomes without notable success) to incubation of freshly drawn cerebrospinal fluid (CSF) from patients with schizophrenia and from normal and neurological control subjects with human neuroblastoma cells. Results of these studies suggest cell transformations by an element in CSF of patients with chronic schizophrenia.